LSO is generally recognized as the ideal scintillator for PET. It has high stopping power for 511 keV gamma rays, high light yield of over 20000 photons/MeV, and rapid decay of 32 ns. It achieves high coincidence timing resolution and energy resolution. But single crystals of LSO are difficult and expensive to grow, reproducibility is poor, and the material is simply not available for general commercial use. To overcome these drawbacks, we have in our previous work developed a translucent LSO optical ceramic, which displays scintillation performance comparable to that of the single crystal, yet is easier to fabricate and could fill the availability gap at lower cost. But because LSO is optically anisotropic, it cannot be made fully transparent by conventional ceramic technology. Recently, however, a new process has been developed through nanotechnology that is capable of achieving virtually full transparency in ceramics of even optically anisotropic materials. The technique involves the consolidation of nanopowders under conditions that limit the ultimate grain sizes to below the wavelengths of visible light, thereby preventing virtually all scattering and rendering the material fully transparent. The procedure has been completely confirmed in experiments on polycrystalline alumina, which is similarly anisotropic, and is being developed for optical window applications. It is the aim of this proposal to combine the two already developed technologies so as to produce LSO in the form of a fully transparent optical ceramic, which displays scintillation performance comparable to that of a single crystal. In Phase I we will confirm that the process that has already been established for alumina is adaptable to LSO as well. We will establish techniques to fabricate the necessary nanoparticulate powders and to define the consolidation conditions under which the desired material properties can be achieved. [unreadable] [unreadable] [unreadable]